The present invention relates to a television camera objective having a driving mechanism for adjusting components of an optical system, and more particularly relates to such an objective including an engaging mechanism for preventing a transmission shaft from rotating in the absence of a driving unit for controlling focusing components.
In usual television camera objectives having a driving mechanism for adjusting components of an optical system, a controlled displacement of at least one component of the optical system is caused by a driving force which, in turn, is transmitted from a driving unit to a lens component displacing mechanism through a transmission shaft. In zoom lenses, in which the focal length is variable, correlative displacements of lens components for varying the focal length and for compensating are attended by variations of magnification ratio. On the other hand the focusing control of an objective is performed by an axial displacement of focusing lens components. In standard television camera objectives, there are provided driving force transmission mechanisms on which driving units identical in their construction are detachably mounted for zooming control and focusing control.
There are two well known types of driving units. One of them is a servo control driving unit, or so-called servo module, into which a servo motor is built for motor-operated zooming control or motor-operated focusing control. The other is a manual control driving unit, or so-called manual module, having a flexible cable through which zooming or focusing control commands are manually given by an operator. Such driving units are a servo module or a manual module are selectively mounted on the driving force transmission mechanism according to the contemplated mode of operation.
Such driving units as described hereinbefore are usually demounted from the driving force transmission mechanism during shipment from the factory or during transportation from one studio to another. Generally, objectives for use with television cameras have an optical system with a large aperture number and components which are quite heavy in weight. Consequently, upon the objective without driving units being inclined, one or more movable lens components can shift in position. Such motions of these movable lenses finally cause the guide pin of a movable lens holder to come into collision with the end of a cam slot formed on a camming cylinder. As a result of that, the guide pin and/or cam slot can be damaged, and the movable lenses can break by impact of the guide pin and movable lens holder.